29th International Cosmic Ray Conference Pune (2005) 00, 101–104

Telescope Array; Progress of Fluorescence Detector
S. Ogio , M. Fukushima , F. Kakimoto and M. Chikawa ,for the Telescope Array Collaboration(a) Graduate School of Science, Osaka City University, Osaka 558-8585, Japan(b) Institute for Cosmic Ray Research, University of Tokyo, Kashiwa 277-8582, Japan(c) Graduate School of Science and Engineering, Tokyo Institute of Technology, Tokyo 152-8550, Japan(d) School of Science and Engineering, Kinki University, Osaka 577-8502, Japan

Presenter: S. Ogio (sogio@sci.osaka-cu.ac.jp), jap-ogio-S-abs2-he15-oral
We start the construction of the fluorescence detector in 2004. At the present time, the construction of the shedof the south-east station is finished, and 12 telescope mounts were placed in the shed. Moreover, the power
generators for the station and one LIDAR system 100m apart from the station are installed. At the same time,
we advance development of the PMT cameras and the electronics. In 2005, we completed the constructions ofa prototype telescope. This telescope has all the elements for detections of fluorescence light. We measured
light pulses from artificial light sources, for development of the electronics, the data acquisition system andthe calibration system. We will start test observations with two mirror–detector system at the first fluorescence
detector station in July 2005.

1.

Introduction

We steadily implement the construction of detectors for the Telescope Array(TA) experiment which measureultra high energy cosmic rays at Utah with strong cooperative activities of Japanese and US researchers. Thesewill become a hybrid detection system which consists of a huge air shower array and an atmospheric fluorescence detector array. In this report, we will offer a broad introduction of fluorescence detectors of TA, and wewill show the results of test observations and the construction schedule.

2.

Telescopes, LIDAR and Laser Facility

The site of the TA experiment is located at Milard county in the state of Utah, and the altitude is about 1500
m. The deployment of TA detectors is shown in Figure 1. The TA fluorescence detector array consists of threetelescope stations, and each station contains 12 telescopes. The stations are placed on edges of the surface
detector array, and the distance between stations is about 40 km. Every station is observing atmosphere above
the array, and the stereoscopic coverage is 97 % of the array area.
Every telescope has a mirror with a diameter of 3.3 m and with a focal length of 2.96 m which is composed of
18 hexagonal shape segment mirrors. The FWHM of an image on the focal plane for a point-like light sourceis less than 30 mm, which is less than half pixel size of the imaging camera.
The imaging camera has a size of 1 m  1 m, and has a close–packed structure of 256 hexagonal PMTs. Thesize of the photo cathode is nearly equivalent to  . Thus one camera has a field of view(FOV) of       .
The viewing fields of adjacent telescopes overlap for about    . Thus for a whole station the elevation anglesof the FOV is    , and the azimuthal viewing angle is about   .
Every PMT has a UV transparent filter, BG3 by Schott, attached on the PMT head, and the front panel of acamera is a UV transparent acrylic plate, Paraglass 00 by Kuraray.
A LIDAR system for TA, which measures atmospheric transparency, mainly consists of of a 355 nm 5 mJ laser,

102S. Ogio et al.

y[km]403020100-10-20-30-40-40-30-20-100102030

40x[km]Figure 1. The left panel is a detector layout drawing for the TA experiment. The green rhombuses indicate the positions ofsurface detectors, and the violet pentagon-shaped markers indicated the locations of the fluorescence stations. The yellow
cross markers are planned positions of radio repeater stations. In the right panel, the arcs shows the viewing areas by thestations projected on the ground, where the radius of the arcs is 40 km. The area filled with green markers is the stereoscopic
coverage area with the stations.

Figure 2. The left panel is an external view of the fluorescence detector station. In this picture the shutter is open, and thena telescope mount held segment mirrors is seen. The right panel is a close–up view of a telescope mount. The lower partof it held segment mirrors and a imaging camera. The picture was taken at a workshop of a production company in Japan.

a 12” light corrector with a 3/4” PMT, a CCD camera for monitoring clouds and data recording electronics.
Every station has the LIDAR system, which installed 100m apart from the telescope building.
In addition to the LIDAR systems, we will install 16 mJ Nd:YAG laser as a standard candle, which is called“Central Laser Facility(CLF)”. The CLF located in equal distances from every stations.

3.

Electronics and DAQ

The block diagram of electronics and DAQ system for a fluorescence station is shown in Figure 3.
The signal induced by photons entering a PMT is amplified by the pre–amplifier attached on the PMT, andfed into a Signal Digitizer/Finder(SDF) module. The gain of the PMTs is adjusted to    and that of thepre–amplifiers is 40. In the SDF the signal travels through shaper–amplifiers, and then is digitized by 12 bits
FADC with the sampling frequency of 40 MHz. Finally, the successive digital values are summed in fours and103

Telescope Array; Progress of Fluorescence ...
PMT camera
Patch Panel
Pre−Amp.
SDF(Signal Digitizer / Finder)
16/mirror
PMTs
Signal Finder
Amp.

FADC

MemoryMirror PC

Track Finder

CTD(Central Trigger Distributor)
1/stationemGUI

Storage PCetworkSharedM

TF(Track Finder)
1/mirrorRun control PC

ory

IRQ
Hit Pattern

Lookup Memory

GPSN

Inter−mirror trigger,
External trigger,
System clock

VMEStation PC

IRQ

Slow control PC
VMELANElectricity
High Vlotage
WeatherShutters
etc.....

Figure 3.

recorded in a memory. As a consequence, the sampling frequency and the resolution for recorded waveforms
corresponds to 10 MHz and 14 bits, respectively.
In the electronics described above, we adjust applied high voltages(HV) for every PMT to the condition inwhich one ADC count is equivalent to 0.2 photo electrons. High voltages are controlled for each PMT as
individual over the range of  V to  ! V. In our HV system, the maximum current is 0.35 mA perchannel and the ripple is less than 50 mVp-p.
The measured linearity of the whole electronics is better than " 1 % over a dynamic range of 0 to 660 p.e./10
ns. Moreover, the measured noise level is less than 1 mV, which is equivalent to 0.4 p.e..
We have implemented the following 3 steps of the triggering processes.
1. SDFs has a hit recognition process for each pixel, which is called 1st level trigger.
2. On a Track Finder(TF) module the 2nd level trigger logic searches tracks in a camera image, which arecompared by pattern recognition algorithm.
3. A Central Trigger Distributor(CTD) module accumulates 2nd level trigger information from all the TF
modules in a station, and determines to generate a final trigger. The final trigger information is distributed
to all the TF modules to initiate readouts of buffered data. Moreover, the final trigger logic on CTD also
recognizes inter–camera tracks and external triggers.
Triggering processes are executed for every sequence of pixel data equivalent to 12.8 #%$ , and this width isshorter than the total processing time for each trigger decision. Farther information for the electronic modules
will be presented in other reports at this conference[1][2] [3][4].
When the DAQ system is triggered, Mirror PCs and the Station PC accumulate data from SDFs, a TF and a
CTD through VME bus and upload data to a file server(Storage PC) through the local area network. On thisserver online analysis processes are running during observation times. The Slow Control PC communicatesmany types of hardwares, such as two power generators, the high voltage controllers for every telescopes,

104

S. Ogio et al.

a weather station, the Xenon flashers for every cameras, the shutter controllers for the building, etc. Everycomputer has own resident process to control operations on each PC, and the resident process on the Run
Control PC has ultimated control over all the processes on every computers. We make interactions between
computers with UNIX/Linux socket programing and use the NSM(Network Shared Memory) package[6] forcommunications between remote processes, which have been developed for the Belle collaboration[5].

4.

Laboratory Tests in Akeno

We have already finished constructions of the first station building, which is located on Black Rock Mesa(BRM),
in 2004, and we have installed the telescope mounts and the LIDAR system in early 2005. Moreover, segment
mirrors has been installed for two telescopes in the station, which optics are adjusted.
Moreover, we produced two sets of photon detectors including the PMT cameras and the electronics (except high voltage controllers), and we executed laboratory tests for these detectors, which are mounted on aproto–type telescope at Akeno observatory during February to May 2005. In these tests we did not observe
atmosphere, and measured photons from the calibrated artificial light sources, such as a Xenon light flasher
and a LED array. Then, we verified that the PMTs and the electronics meet specifications and measured noiselevels in the electronics. Moreover, we checked cabling, hardware logic programs and performances of DAQ
and high voltage control processes.

5.

Conclusions

After the laboratory tests, we sent these sets of the detectors to Utah. The cameras and the electronics will beinstalled on telescopes in the BRM station in June, and we will test all the mirror–detector system and willobserve side–scattered photons emitted by the LIDAR system and fluorescence light induced by air showers.
At this Conference, we will present the results of these test observations.
In parallel with the test observations, we continue productions of mirrors, PMTs and electronics, and constructions of other stations. The installations of all the station will be completed by the spring of 2007.
This work is supported in part by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology in Japan. We would like to thank the Millard County Council andFillmore BLM.

References[1] A. Taketa, et al., 29th ICRC, Pune (2005).
[2] A. Tameda, et al., 29th ICRC, Pune (2005).
[3] H. Tokuno, et al., 29th ICRC, Pune (2005).
[4] M. Chikawa, et al., 29th ICRC, Pune (2005).
[5] The Belle collaboration, http://belle.kek.jp[6] M. Nakao and S. Y. Suzuki, IEEE Transactions on Nuclear Science, 47,2 (2000).